Conventionally, in order to move an object in the three degrees of freedom defined by planar motion, it was necessary to employ three individual linear and/or rotary motors, each driving a single axis stage with the stages cascaded in series with each other. This required a number of appliances with a plurality of bearings supporting large masses which move in different directions, each bearing having unwanted compliances. This resulted in resonances, friction, backlash and inaccuracy of movement. The lowest mode resonant frequency tended to be much lower than desirable, making high accuracy servo control difficult.
Accordingly, it is a primary object of the present invention to provide a new and improved alignment apparatus, which will become apparent as the description proceeds.